Leakage dielectric waveguide and plane antenna using said leakage dielectric waveguide

Abstract: A leakage dielectric waveguide includes a housing made of plane-shaped parallel electrical conductors (1,2) provided so as to be parallel to each other, and a dielectric strip (3) for propagating a high-frequency wave between the parallel electrical conductors (1,2), wherein the dielectric strip (3) is provided within the housing. The housing is arranged to be asymmetrical (2 s ), thereby leaking and radiating a high-frequency wave propagating through the dielectric strip (3). Further, the housing is preferably further composed of the plane-shaped parallel electrical conductors (1,2) and a side wall (4). Further, a plane antenna (10) can be constituted by the above-mentioned leakage dielectric waveguide, and projecting means, in response to the high-frequency wave projected from the dielectric waveguide, for projecting the high-frequency wave toward free space.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leakage dielectric waveguide according to the preamble of claim 1 and a plane antenna using the leakage dielectric waveguide, and particularly to a leakage dielectric waveguide for leaking and radiating a high-frequency wave and a plane antenna using the leakage dielectric waveguide. In the specification, the term ,,high-frequency waves" means microwaves, quasi-millimeter waves, or millimeter waves which have a frequency higher than approximately 1 GHz. A leakage dielectricwaveguide according to the preamble of claim 1 is shown in ,,Electronics and Communications in Japan, part II: Electronics", .No. 2,. Feb. 1991, NY, US; Yoneyama: ,,Millimeter-Wave Integrated Circuits Using Nonradiative Dielectric Waveguide". 2. Description of the Prior Art As a dielectric waveguide for millimeter wave integrated circuits, there has been conventionally known to those skilled in the art, a nonradiative dielectric waveguide (hereinafter, referred to as an NRD waveguide), in which a dielectric strip is sandwiched between upper and lower metal plates. The conventional NRD waveguide is disclosed in, for example, Japanese Patent Examined Publication No. 1-51202. In the NRD waveguide, there has been proposed a leakage NRD waveguide (hereinhafter, referred to as a conventional leakage NRD waveguide), in which the dielectric strip is provided with a plurality of recessed portions at intervals of a propagation wavelength of electromagnetic waves λg. In this case, when a millimeter wave signal is applied to an end of the NRD waveguide for excitation, and then the millimeter wave signal is leaked between the upper and lower metal plates so that radiation is accomplished. The conventional NRD waveguide is disclosed in, for example, Tsukasa Yoneyama et al., "Leakage Wave NRD waveguide of Broadside Radiation", the Proceedings of Spring Meeting of the Institute of the Electronics, Information, and Communications Engineers, in Japan, as published on March 15, 1992. Further, there is also proposed a plane antenna, in which the conventional leakage NRD waveguide and a slot antenna are combined together with each other. This is disclosed in, for example, Toshihiko Agatsuma et al., "Preliminary Experiments on Plane Antenna with Transmission Lines of Leakage Wave NRD waveguides", the Proceedings of Spring Meeting of the Institute of the Electronics, Information, and Communications Engineers, in Japan, as published on March 15, 1992. However, in order to provide the recessed portions in the dielectric strip, it is necessary to perform an extremely complex manufacturing process. This results in expensive manufacturing cost. Further, reflected waves may be generated in a plurality of recessed portions formed in the dielectric strip. This leads to that it is difficult to perform successful impedance matching. Then, this causes deterioration in the frequency characteristic of input impedance, and this results in a narrower usable bandwidth depending on the number of the recessed portions. Accordingly, the plane antenna, comprising both of the conventional leakage NRD waveguide and a slot antenna which are combined together with each other, has a relatively narrow operating bandwidth and a relatively low radiation efficiency, disadvantageously. SUMMARY OF THE INVENTION An object of the present invention is therefore to provide a leakage dielectric waveguide capable of being manufactured using a manufacturing process simpler than the conventional manufacturing process with an inexpensive cost, and capable of operating over wider bandwidth and projecting radio waves with a radiation efficiency higher than those of the conventional ones, Another object of the present invention is to provide a plane antenna using the above-mentioned leakage dielectric waveguide, capable of being manufactured using a manufacturing process simpler than the conventional manufacturing process with an inexpensive cost, and capable of operating over wider bandwidth and projecting radio waves with a radiation efficiency higher than those of the conventional ones. In order to achieve the aforementioned objective, according to one aspect of the present invention, there is provided a leakage dielectric waveguide according to claim 1. Further, according to preferred embodiments of the present invention, said leakage dielectric waveguide comprises: upper and lower parallel electrical conductors provided so as to be parallel to each other; said dielectric strip for propagating a high-frequency wave between said parallel electrical conductors, said dielectric strip being provided between said upper and lower parallel electrical conductors: and said vertically asymmetrical housing for leaking and radiating said high-frequency wave propagating through said dielectric strip, said housing being provided on either one of both sides and one side of said dielectric strip. In the above-mentioned leakage dielectric waveguide said asymmetrical housing preferably includes a step formed in said housing. In the above-mentioned leakage dielectric waveguide, said asymmetrical housing preferably includes a further dielectric strip which is formed on said housing so as to be apart from said dielectric strip and so that the longitudinal direction of said dielectric strip is parallel to that of said further dielectric strip. In the above-mentioned leakage dielectric waveguide, said asymmetrical housing preferably includes a microstrip line which is formed on said housing so as to be apart from said dielectric strip and so that the longitudinal direction of said dielectric strip is parallel to that of said microstrip line. In the above-mentioned leakage dielectric waveguide, said asymmetrical housing preferably includes a projecting electrical conductor which is formed on said housing so as to vertically project into the inner part of said housing. In the above-mentioned leakage dielectric waveguide, said asymmetrical housing preferably includes a dielectric slab formed on said housing so as to be apart from said dielectric strip and so that the longitudinal direction of said dielectric slab is perpendicular to that of said dielectric strip. In the above-mentioned leakage dielectric waveguide, said asymmetrical housing preferably includes a plurality of dielectric slabs which are formed in parallel to each other at intervals of a propagation wavelength of said high-frequency wave on one inner surface of said housing so as to be apart from said dielectric strip and so that the longitudinal direction of said dielectric slabs is perpendicular to that of said dielectric strip. In the above-mentioned leakage dielectric waveguide, said asymmetrical housing preferably includes a plurality of first dielectric slabs and a plurality of second dielectric slabs, wherein said plurality of first dielectric slabs are formed in parallel to each other at intervals of a propagation wavelength of said high-frequency wave, on one inner surface of said housing so as to be apart from said dielectric strip and so that the longitudinal direction of said first dielectric slabs is perpendicular to that of said dielectric strip, and wherein said plurality of second dielectric slabs are formed in parallel to each other at intervals of a propagation wavelength of said high-frequency wave and at half the position in the horizontal direction of said plurality of first dielectric slabs, on another inner surface of said housing so as to be apart from said dielectric strip and so that the longitudinal direction of said second dielectric slabs is perpendicular to that of said dielectric strip. In the above-mentioned leakage dielectric waveguide, said housing further preferably comprises a side wall. According to a further aspect of the present invention, the leakage dielectric waveguide further comprises deflection means for deflecting a direction of radiation of the leaked and radiated high-frequency wave toward a predetermined direction. According to a still further aspect of the present invention, in the above-mentioned leakage dielectric waveguide, said housing preferably includes deflection means for deflecting a direction of radiation of said leaked and radiated high-frequency wave toward a predetermined direction. In the above-mentioned leakage dielectric waveguide, said deflection means is preferably a dielectric prism. In the above-mentioned leakage dielectric waveguide, said dielectric strip and said housing are preferably arranged so that the leaked and radiated high-frequency wave is radiated toward a predetermined direction of radiation. According to a still more further aspect of the present invention, there is provided a plane antenna comprising the features of claim 16. According to a preferred embodiment of the present invention, there are provided the followings: (a) a leakage dielectric waveguide having a dielectric strip provided within a housing composed of plane-shaped parallel electrical conductors, wherein the housing is arranged to be asymmetrical so that a high-frequency wave that propagates through the dielectric strip is leaked and radiated; (b) a dielectric waveguide having a dielectric strip provided within a housing composed of plane-shaped parallel electrical conductors and side walls, wherein the housing is arranged to be asymmetrical so that a high-frequency wave that propagates through the dielectric strip is leaked and radiated; and (c) a dielectric waveguide having a dielectric strip sandwiched between upper and lower parallel electrical conductors, wherein a vertically asymmetrical housing for leaking and radiating a high-frequency wave that propagates through the dielectric strip is provided on both sides or one side of the dielectric strip. Accordingly, the dielectric strip is not provided with recessed portions unlike the conventional one, but is provided with only an asymmetrical housing. As a result, the manufacturing process becomes simple and the manufacturing cost can be reduced. Besides, since the dielectric strip is not provided with a plurality of recessed portions, unnecessary waves can be suppressed, so that frequency characteristic of input impedance can be improved and wider-bandwidth operation can be realized. Further, according to the present invention, there is provided a leakage dielectric waveguide further comprising deflection means for deflecting the direction of radiation of a leaked and radiated high-frequency wave toward a predetermined direction, wherein the housing includes deflection means for deflecting the direction of radiation of a leaked and radiated high-frequency wave toward a predetermined direction or wherein the dielectric strip and the housing are so arranged that the leaked and radiated high-frequency wave is radiated toward a predetermined direction. With this arrangement, the radiated high-frequency wave can be deflected toward the same direction so as to be radiated with high radiation efficiency in a state of a substantially uniform electric field distribution and almost no residual power. Still further, according to present invention, there are provided plane antennas in which the abovementioned leakage dielectric waveguide is combined with means for radiating a leaked and radiated high-frequency wave into free space. In this arrangement, a plane antenna which operates in wider bandwidth and with higher efficiency can be implemented, compared with the conventional plane antenna. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings throughout which like parts are designated by like reference numerals, and in which: FIG. 1 is a plan view of a plane antenna apparatus using a leakage NRD waveguide, which is a first preferred embodiment according to the present invention; FIG. 2 is a plan view of the plane antenna apparatus of FIG. 1; FIG. 3 is a longitudinal sectional view taken along a line III - III' of FIG. 2; FIG. 4 is a longitudinal sectional view of a plane antenna apparatus using a leakage NRD waveguide, which is a first modification of the first preferred embodiment according to the present invention; FIG. 5 is a longitudinal sectional view of a plane antenna apparatus using a leakage NRD waveguide, which is a second modification of the first preferred embodiment according to the present invention; FIG. 6 is a longitudinal sectional view showing electric field strength in proximity to the leakage NRD waveguide, which is provided for explaining an operation of leakage radiation in the leakage NRD waveguide of the first preferred embodiment; FIG. 7 is a plan view showing electric field strength in proximity to the leakage NRD waveguide with an electrical conductor plate 1 removed, which is provided for explaining a direction in which electromagnetic waves are radiated from the leakage NRD waveguide of the first preferred embodiment; FIG. 8 is a longitudinal sectional view of a leakage NRD waveguide, which is a third modification of the first preferred embodiment according to the present invention; FIG. 9 is a longitudinal sectional view of a leakage NRD waveguide, which is a fourth preferred embodiment according to the present invention; FIG. 10 is a longitudinal sectional view of a leakage NRD waveguide, which is a fifth modification of the first preferred embodiment according to the present invention; FIG. 11 is a longitudinal sectional view of a leakage NRD waveguide, which is a sixth modification of the first preferred embodiment according to the present invention; FIG. 12 is a longitudinal sectional view of a leakage NRD waveguide, which is a seventh modification of the first preferred embodiment according to the present invention; FIG. 13 is a perspective view of a leakage NRD waveguide, which is an eighth modification of the first preferred embodiment according to the present invention; FIG. 14 is a longitudinal sectional view taken along a line XIV - XIV' of FIG. 13; FIG. 15 is a longitudinal sectional view of a leakage NRD waveguide, which is a ninth modification of the first preferred embodiment according to the present invention; FIG. 16A is a plan view of a plane antenna apparatus using the leakage NRD waveguide, which is a second preferred embodiment according to the present invention, wherein the electrical conductor plate 1 has been removed; FIG. 16B is a longitudinal sectional view taken along a line XVIB - XVIB' of FIG. 16A; FIG. 17A is a plan view of the plane antenna apparatus using the leakage NRD waveguide of FIGs. 16A and 16B; FIG. 17B is a longitudinal sectional view taken along a line XVIIB - XVIIB' of FIG. 17A; FIG. 18A is a plan view of the plane antenna apparatus using the leakage NRD waveguide which is a modification of the second preferred embodiment, wherein the electrical conductor plate 1 has been removed; FIG. 18B is a longitudinal sectional view taken along a lineXVIIIB - XVIIIB' of FIG. 18A; FIG. 19A is a plan view of a plane antenna apparatus using the leakage NRD waveguide which is a third preferred embodiment according to the present invention, wherein the electrical conductor plate 1 has been removed; and FIG. 19B is a longitudinal sectional view taken along a line XIXB - XIXB' of FIG. 19A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments according to the present invention are described hereinbelow with reference to the accompanying drawings. Generally, homogeneous NRD waveguides are the dielectric waveguides which do not effect radiation in the hybrid transmission mode, however, the preferred embodiments according to the present invention have the following features. In an NRD waveguide having a dielectric strip 3 sandwiched between upper and lower electrical conductor plates 1 and 2, for example, a step 2s is formed in the lower electrical conductor plate 2 as shown in FIG. 8, at portions on the left or right side or both sides of the dielectric strip 3 in a direction perpendicular to the longitudinal direction of the dielectric strip 3, so that the vertical symmetry of the waveguide housing structure is impaired, i.e. a vertically asymmetrical housing is provided. Then a leakage high-frequency high-frequency wave is leaked and radiated which is of a signal transmitted in the NRD waveguide. Hereinafter, an NRD waveguide which leaks and radiates a leakage high-frequency wave is referred to as a leakage NRD waveguide. <First preferred embodiment> FIG. 1 is a plan view of a plane antenna apparatus using a leakage NRD waveguide which is a first preferred embodiment according to the present invention, in which the electrical conductor plate 1 has been removed. FIG. 2 is a plan view of the plane antenna apparatus of FIG. 1. FIG. 3 is a longitudinal sectional view taken along a line III - III' of FIG. 2. In these figures, the longitudinal direction of the dielectric strip 3 of the NRD waveguide is taken as the Z-axis direction, the direction perpendicular to the Z-axis direction in the plan view of FIG. 1 is taken as the X-axis direction, and the direction perpendicular to both the Z-axis direction and X-axis direction is taken as the Y-axis direction. The plane antenna apparatus using the leakage NRD waveguide of the first preferred embodiment, as shown in FIGs. 1 through 3, comprises a leakage NRD waveguide and a slot antenna 10. The features of the leakage NRD waveguide are as follows. The step 2s for radiating a leakage high-frequency wave is formed in the electrical conductor plate 2 at a position which is a predetermined distance away from the dielectric strip 3 and at which the strength of electric field generated by a high-frequency signal transmitted by the dielectric strip 3 is relatively high, in parallel to the longitudinal direction of the dielectric strip 3 which is the Z-axis direction. Further, a dielectric prism 5 for deflecting the direction of radiation of the leakage high-frequency wave toward a direction perpendicular to the longitudinal direction of the dielectric strip 3 is provided at a position which is further away from the dielectric strip 3. As shown in FIG. 3, the dielectric strip 3 is sandwiched between the upper and lower plane-shaped electrical conductor plates 1 and 2 which are parallel to each other. At an edge portion of the electrical conductor plates 1 and 2 which are a predetermined distance away from the dielectric strip 3 in a direction perpendicular to the longitudinal direction of the dielectric strip 3 and besides in the leftward direction in the sectional view of FIG. 3, a reflection plate 4 made of a metal electrical conductor plate is provided so as to oppose to and parallel to the left side surface of the dielectric strip . The above-mentioned leftward direction is the negative direction of X-axis, and hereinafter, the leftward direction is referred to as a direction leftward from the dielectric strip 3 in the plan views or sectional views, while the rightward direction is referred to as a direction rightward from the dielectric strip 3 in the plan views or sectional views. Meanwhile, in the electrical conductor plate 2 at a position which is a predetermined distance away from the dielectric strip 3 in a direction perpendicular to the longitudinal direction of the dielectric strip 3 and besides in the rightward direction and which is parallel to the longitudinal direction of the dielectric strip 3, a one-in-number staircase-like step 2s is formed so as to rise in a direction perpendicular to the plane of the electrical conductor plate 2 and to shorten the distance between the upper and lower electrical conductor plates 1 and 2. The distance between the electrical conductor plates 1 and 2 is kept as it is at any position rightward of the step 2s. When a high-frequency signal is fed to the dielectric strip 3 in the direction indicated by an arrow 50 which is the Z-axis direction, the high-frequency signal propagates through the dielectric strip 3 in the z-axis direction. In this case, the distribution of electric field strength in the dielectric strip 3 and in the vicinity thereof is as shown in FIG. 6. To effectively reflect a leakage high-frequency wave leaked leftward of the dielectric strip 3 toward the rightward direction and to effectively radiate the leakage high-frequency wave radiated at the step 2s, it is preferable that the position where the reflection plate 4 is located and the position where the step 2s is formed are such that the electric field strength generated by the high-frequency signal transmitted by the NRD waveguide is relatively high. The dielectric strip 3 is a dielectric material which is low in loss at high frequencies, such as Teflon, polyethylene, polystyrene, or the like, having a dielectric constant ε r1 sufficiently higher than the dielectric constant of air ε r0 . When the dielectric strip 3 has a height a and width b, if the wavelength of free space is λ, then the following equations (1) and (2) are effected: a λ ≒0.45 and ε rp · b λ ≒0.5 where ε rp is the square root of (ε r - 1). In addition, the terminating portion of the dielectric strip 3 on the upper side in FIG. 1 and FIG. 2 is terminated by a resistive terminator (not shown). However, the present invention is not limited to this, and the terminating portion of the dielectric strip 3 is not necessarily required to be terminated by a resistive terminator. Further, a dielectric prism 5 for deflecting the direction of radiation of the leakage high-frequency wave toward a direction perpendicular to the longitudinal direction of the dielectric strip 3 is formed to be charged therein so as to be sandwiched at a position which is a predetermined distance away from the formation position of the step 2s in the rightward direction thereof and which is leftward of the formation position of the slot antenna 10. The dielectric prism 5 is made of a dielectric material such as Teflon having a dielectric constant ε r2 . The left-side surface of the dielectric prism 5 is a plane of incidence which the leakage high-frequency wave is to enter, as will be described in detail later, wherein a plurality of recessed portions are formed so as to be shaped into a sawtooth wave or a triangular wave in the plan view of FIG. 1 so that a zoning is formed at a prism angle  ds . On the other hand, the right-side surface of the dielectric prism 5 is an outgoing plane through which the leakage high-frequency wave having been incident into the dielectric prism 5 goes out, wherein the outgoing plane is provided so as to be parallel to the right and left surfaces of the dielectric strip 3. When the dielectric strip 3 of the NRD waveguide has an effective dielectric constant ε e , then a prism angle  ds and a zoning depth t of the dielectric prism 5 are represented by the following Equations (3) and (4), respectively: tan ( ds ) = ε e ε r2 -(1- ε e ) and t = λ ε r2 -1 As apparent from the above Equation 3 and Equation 4, when a dielectric material having a relatively large dielectric constant ε r2 is used as the material of the dielectric prism 5, the prism angle  ds and zoning depth t can be reduced, which is advantageous in the actual manufacturing process. Also, as shown in FIG. 2 and FIG. 3, the slot antenna 10 is formed on the right side of the dielectric prism 5. The slot antenna 10 comprises a plurality of rectangular slots 11, the longitudinal direction of which is parallel to the longitudinal direction of the dielectric strip 3, and which are formed in the upper grounded electrical conductor plate 1 at intervals of one wavelength of the standing wave. In addition, a reflection plate (not shown) made of a metal plate is sandwiched between right ends of the upper and lower electrical conductor plates 1 and 2, which are located in the right side of the slot antenna 10, so as to oppose to the reflection plate 4. An operation of the plane antenna apparatus using the leakage NRD waveguide of the first preferred embodiment constructed as described above is now described in detail. As shown in FIG. 1 and FIG. 7, when a high-frequency signal is applied to the dielectric strip 3 in the direction of the arrow 50, which is the Z-axis direction, the high-frequency signal propagates through the dielectric strip 3 in the Z-axis direction. Since the dielectric constant ε r1 of the dielectric strip 3 is greater than the dielectric constant ε r0 of the air layers on both sides of the dielectric strip 3, a phase velocity v1 of the propagating high-frequency wave is higher than a phase velocity v2 of the leakage high-frequency wave. Accordingly, the leakage high-frequency wave propagates leaking rightward and leftward from the dielectric strip 3. For example, with regard to the leakage high-frequency wave propagating rightward, a point at which the phase at C point of the high-frequency wave that has leaked from A point and the phase of the high-frequency wave that has been leaked from D point coincident with each other is, for example, an F point. That is, the leakage high-frequency wave progresses at a radiation angle p (< 90°) with respect to the Z-axis, propagating as a plane wave. On the other hand, the leakage high-frequency wave that has been leaked and radiated leftward from the dielectric strip 3 is reflected by the reflection plate 4, and thereafter is reflected toward the dielectric strip 3, passing the dielectric strip 3 and propagating rightward from the dielectric strip 3. Then at the step 2s, as shown in FIG. 1 and FIG. 3, an electric field is generated between the upper and lower electrical conductor plates 1 and 2 in the vertical direction which is the Y-axis direction, due to the housing structure vertically asymmetrical at the position. As a result, a leakage high-frequency wave is leaked and radiated, propagating between the upper and lower electrical conductor plates 1 and 2 while holding a radiation angle g equal to the radiation angle p. Further, the leakage high-frequency wave enters the zoned plane of incidence of the dielectric prism 5 in the direction of an arrow 51 at an angle of incidence in (< 90°), and thereafter is refracted by the plane of incidence, propagating through the dielectric prism 5 in a direction of an arrow 52 which is the X-axis direction perpendicular to the longitudinal direction of the dielectric strip 3, i.e. at an angle out (  in <  out < 90°,  ds +  out = 90°) with respect to the plane of incidence. Then, the leakage high-frequency wave goes out in a direction perpendicular to the outgoing surface of the dielectric prism 5, propagating between the upper and lower electrical conductor plates 1 and 2 with a high radiation efficiency in a state of substantially uniform electric field distribution and almost no residual power. Subsequently, the leakage high-frequency wave of plane wave enters the slot antenna 10 and propagates in the space under the array of the rectangular slots 11, and reflected by the right-end reflection plate (not shown). Therefore, the leakage high-frequency wave between the upper and lower electrical conductor plates 1 and 2 in the slot antenna 10 results in a standing-wave distribution. At this point, the leakage high-frequency wave excites the array of slots 11 arrayed in parallel to the dielectric strip 3. Since the plurality of slots 11 are formed at intervals of one wavelength of the standing wave and positioned so that their magnetic fields become the largest, the slots 11 are excited in phase while the longitudinal direction of the slots 11 is also excited in phase. Accordingly, the electromagnetic waves of the leakage high-frequency waves are radiated toward the free space as linearly polarized wave in the upward direction in the plan view of radiation perpendicular to the plane of the electrical conductor plate 1. In the leakage NRD waveguide constructed as described above, the dielectric strip 3 is not provided with such any recessed portion as formed in the conventional one, but is provided with only the step 2s in the electrical conductor plate 2. As a result, the manufacturing process becomes simple and the manufacturing cost can be reduced. Further, since the dielectric prism 5 is not provided with a plurality of recessed portions, unnecessary reflected waves can be suppressed, so that the frequency characteristic of the input impedance can be improved and also a wider bandwidth operation can be realized. Further, by provision of the dielectric prism 5, the leakage high-frequency wave that has been leaked and radiated can be deflected in the same direction and then can be radiated with high radiation efficiency in a state of substantially uniform electric field distribution and almost no residual power. Still further, by combining the leakage NRD waveguide and the slot antenna 10 together, there can be provided the plane antenna apparatus which operates in wider bandwidth and with higher efficiency, as compared with the conventional leakage NRD waveguide. In the above first preferred embodiment, the dielectric prism 5 is formed to be charged therein at a position between the step 2s and the slot antenna 10. However, the present invention is not limited to this positioning of the dielectric prism 5, and a partial portion of the dielectric prism 5 other than the zoned portion thereof may be formed to be charged up to the position of the slot antenna 10. By this arrangement, the grating lobe in the radiation directivity characteristic of the leakage NRD waveguide can be reduced. Further, as shown in FIG. 5, a tapered portion may be provided on the outgoing surface of the dielectric prism 5 so that the length of the dielectric prism 5 on the electrical conductor plate 2 side in the X-axis direction is longer than that on the electrical conductor plate 1 side. Still further, a tapered portion may be provided at the step 2s so that the distance between the upper and lower electrical conductor plates 1 and 2 becomes shorter gradually. By this arrangement, the side lobe in the radiation directivity characteristic of the leakage NRD waveguide can be reduced. In the above-described preferred embodiments, the leakage NRD waveguide has the step 2s formed in the lower electrical conductor plate 2 as a structure for leaking and radiating a leakage high-frequency wave. However, the present invention is not limited to this, but the present invention may be a waveguide housing structure as shown in the followings (a) through (d): (a) As shown in FIG. 9, a dielectric strip 6 may be provided on the electrical conductor plate 1 on the right side of the dielectric strip 3 in parallel to the longitudinal direction of the dielectric strip 3 and a predetermined distance away from the dielectric strip 3; (b) As shown in FIG. 10, a microstrip line may be provided by forming a strip-shaped dielectric strip 6 on the electrical conductor plate 1 on the right side of the dielectric strip 3 so as to have a longitudinal direction parallel to the dielectric strip 3 and by further forming a strip electrical conductor 70 on the dielectric strip 6; (c) As shown in FIG. 11, a dielectric slab 7 having a longitudinal direction perpendicular to the dielectric strip 3 may be provided on the electrical conductor plate 1 on the right side of the dielectric strip 3 so as to be a predetermined distance away from the dielectric strip 3. In this case, the leakage NRD waveguide operates in such a manner that a leakage high-frequency wave is radiated by the dielectric slab 7 in a direction tilted with respect to the longitudinal direction of the dielectric strip 3. Further, to radiate and propagate the leakage high-frequency wave more efficiently, a plurality of dielectric slabs 7 may be provided on the electrical conductor plate 1 on the right side of the dielectric strip 3 in a periodic structure at intervals of a propagation wavelength λg so as to each have a longitudinal direction parallel to the direction perpendicular to the dielectric strip 3 and to be parallel to one another, as shown in FIG. 13 and FIG. 14. Still further, a plurality of dielectric strips 8 may be provided on the lower surface of the upper electrical conductor plate 1 in a periodic structure so as to be parallel to the plurality of dielectric slabs 7 and to be spaced from the dielectric slabs 7 each at an interval of λg/2 and besides spaced from one another at intervals of a propagation wavelength λg, as shown in FIG. 15; and (d) As shown in FIG. 12, a protruding or projecting electrical conductor 2p may be provided so as to vertically protrude or project into the inner part of the housing from the electrical conductor plate 2 on the right-side surface of the dielectric strip 3. <Second preferred embodiment> FIG. 16A is a plan view of a plane antenna apparatus using a leakage NRD waveguide which is a second preferred embodiment according to the present invention, in which the electrical conductor plate 1 has been removed, and FIG. 16B is a longitudinal sectional view take along a line XVIB - XVIB'. Further, FIG. 17A is a plan view of a plane antenna apparatus using the leakage NRD waveguide of FIGs. 16A and 16B, and FIG. 17B is a longitudinal sectional view taken along a line XVIIB - XVIIB'. The features of the plane antenna apparatus of the second preferred embodiment are as follows. Two plane antennas (hereinafter, referred to as plane antenna units) each comprising both of the leakage NRD waveguide and the slot antenna of the first preferred embodiment are arranged integrally so that dielectric strips 3a and 3b perpendicularly cross each other, wherein a grating slot antenna 20, comprising an array of a plurality of rectangular slots 11a and an array of a plurality of rectangular slots 11b both of which are formed perpendicularly to each other and integrally with the upper electrical conductor plate 1, is provided as a radiation antenna. As shown in FIG. 16A, in one plane antenna unit, between the upper and lower electrical conductor plates 1 and 2 and between a left-end reflection plate 4a and a right-end reflection plate 4c in the plan view, there are sequentially formed a dielectric strip 3a, a step 2sa, a dielectric prism 5a, an array of a plurality of rectangular slots 11a, and the reflection plate 4c, in the order from left end to right, in a manner similar to that of the first preferred embodiment. Meanwhile, in another plane antenna unit, between the upper and lower electrical conductor plates 1 and 2 and between a lower-end reflection plate 4b and an upper-end reflection plate 4d in the plan view, there are sequentially formed a dielectric strip 3b, a step 2sb, a dielectric prism 5b, an array of a plurality of rectangular slots 11b, and the reflection plate 4b, in the order from lower end to upward, in a manner similar to that of the first preferred embodiment. In the grating slot antenna 20, the plurality of slots 11a are formed at intervals of the wavelength of standing wave λ so that their longitudinal direction is parallel to the longitudinal direction of the dielectric strip 3a. Meanwhile, the plurality of slots 11b are formed at intervals of the wavelength of standing wave λ so that their longitudinal direction is parallel to the longitudinal direction of the dielectric strip 3b. By this arrangement, the array of the slots 11a and the array of the slots 11b are grated or formes a grating as shown in FIG. 17A. On the entire surface of the electrical conductor plate 1, there is further provided a radome 9 which passes therethrough high frequencies waves and which is made of a resin material such as PC (polycarbonate), PBT (polybutylene terephthalate), FRPP (fiber reinforced polypropylene) or the like. Further, a center electrical conductor 31a of a coaxial cable 30a is inserted at a lower end of the dielectric strip 3a, so that a first high-frequency signal is applied to the dielectric strip 3a through the coaxial cable 30a. Meanwhile, a center electrical conductor 31b of a coaxial cable 30b is inserted at a left end of the dielectric strip 3b, so that a second high-frequency signal is applied to the dielectric strip 3b through the coaxial cable 30b. In the plane antenna apparatus of the second preferred embodiment constructed as described above, when first and second high-frequency signals having a phase difference of 90° therebetween are applied to the dielectric strips 3a and 3b through the coaxial cables 30a and 30b, respectively, then, in a manner similar to that of the first preferred embodiment, the first leakage high-frequency wave which has been leaked from the dielectric strip 3a and radiated by the step 2sa is deflected by the dielectric prism 5a so as to be transmit in the X-axis direction perpendicular to the longitudinal direction of the dielectric strip 3a, entering the grating slot antenna 20 so as to excite the array of the rectangular slots 11a. On the other hand, the second leakage high-frequency wave which has been leaked from the dielectric strip 3b and radiated by the step 2sb is deflected by the dielectric prism 5b so as to transmit in the Z-axis direction perpendicular to the longitudinal direction of the dielectric strip 3b, entering the grating slot antenna 20 so as to excite the array of the rectangular slots 11b. As a result, the high-frequency electromagnetic waves of linearly polarized wave are radiated from the plane antenna units in a direction perpendicular to the surface of the electrical conductor plate 1. In this case, since the first and second high-frequency signals for effecting the above-described excitation have a phase difference of 90° therebetween, there are projected the high-frequency electromagnetic waves of clockwise or counterclockwise circularly polarized waves, in a manner known to those skilled in the art. In the above-described second preferred embodiment, it has been arranged that circularly polarized waves are radiated. However, the present invention being not limited to this, it is also possible that two plane antenna units are arranged so that the respective resonance frequencies of the two plane antenna units are different from each other. In this case, two high-frequency signals having respective frequencies substantially equal to the two resonance frequencies thereof may be applied to the grating slot antenna 20 for excitation. In such a case, the plane antenna apparatus serves as a plane antenna apparatus of linearly polarized waves of two frequencies. FIG. 18A is a plan view of a plane antenna apparatus using a leakage NRD waveguide which is a modification of the second preferred embodiment, in which the electrical conductor plate 1 has been removed. FIG. 18B is a longitudinal sectional view of the plane antenna apparatus taken along a line XVIIIB - XVIIIB'. The features of the modification of the second preferred embodiment are as follows, as compared with the second preferred embodiment. The lower end of the dielectric strip 3a and the left end of the dielectric strip 3b are extended up to on their corresponding other substrates so that an electric power is supplied through the dielectric strips 3a and 3b. <Third preferred embodiment> FIG. 19A is a plan view of a plane antenna apparatus using a leakage NRD waveguide which is a third preferred embodiment according to the present invention, in which the electrical conductor plate 1 has been removed. FIG. 19B is a longitudinal sectional view taken along a line XIXB - XIXB'. The features of the third preferred embodiment are as follows, as compared with the second preferred embodiment. The dielectric prisms 5a and 5b are not provided, and then the longitudinal directions of the dielectric strip 3a and the step 2sa are inclined with respect to the longitudinal direction of the array of the slots 11a of the grating slot antenna 20 by an inclination angle pp, while the longitudinal directions of the dielectric strip 3b and the step 2sb are inclined with respect to the longitudinal direction of the array of the slots 11b of the grating slot antenna 20 by a tilt angle pp. In this case, the inclination angle pp is set substantially equal to the radiation angle p of FIG. 7 and the radiation angle g of FIG. 1. In addition to this, the longitudinal direction of the dielectric strip 3a and the longitudinal direction of the formation position of the step 2sa are parallel to each other, while the longitudinal direction of the dielectric strip 3b and the longitudinal direction of the formation position of the step 2sb are parallel to each other. By the above arrangement, the first and second leakage high-frequency waves leaked from the dielectric strips 3a and 3b and radiated by the steps 2sa and 2sb, respectively, and then enter the grating slot antenna 20 in the directions perpendicular to the array of the slots 11a and the array of the slots 11b of the grating slot antenna 20, respectively, resulting in exciting the arrays of slots in a manner similar to that of the second preferred embodiment. That is, the operation of the third preferred embodiment is substantially the same as the second preferred embodiment, except that deflection by the dielectric prisms 5a and 5b is not effected. The third preferred embodiment as described above is provided with two plane antenna units. However, the present invention is not limited to this, and it may also be provided with only one plane antenna unit. Further, in the second and third preferred embodiments, there have been provided two sets of plane antennas, one set of which comprises one leakage NRD waveguide and one plane antenna unit. However, the present invention is not limited to this, it is also allowed that three or more sets of plane antennas are provided. <Other preferred embodiments> In the above-described preferred embodiments, the electrical conductor plates 1 and 2 have been used. However, the present invention is not limited to this, it may also be arranged that a electrical conductor layer or a electrical conductor film is formed on a dielectric substrate made of a dielectric material having a dielectric constant substantially smaller than the dielectric constant ε r1 of the dielectric strips 3, 3a and 3b, i.e. a printed circuit board may also be used. In the above-described preferred embodiments, it has been arranged to have a housing structure vertically asymmetrical only at one side of the dielectric strips 3, 3a and 3b. However, the present invention is not limited to this, it may also be arranged to have a housing structure vertically asymmetrical at both sides of the dielectric strips 3, 3a and 3b. In the above-described preferred embodiments, there have been used a slot antenna or a grating slot antenna comprising a plurality of slots 11 formed in parallel to one another. However, the present invention is not limited to this, it is also possible to use a cross-shaped slot antenna, a rectangular slot antenna, or other slot antennas, or other types of plane antennas. Further, it is possible to form slots in the electrical conductor plate 1 and form a microstrip patch antenna thereon with a dielectric layer interposed therebetween. As described above in detail, according to the preferred embodiments of the present invention, there are provided the followings: (a) a leakage dielectric waveguide having a dielectric strip provided within a housing composed of plane-shaped parallel electrical conductors, wherein the housing is arranged to be asymmetrical so that a high-frequency wave that propagates through the dielectric strip is leaked and radiated; (b) a dielectric waveguide having a dielectric strip provided within a housing composed of plane-shaped parallel electrical conductors and side walls, wherein the housing is arranged to be asymmetrical so that a high-frequency wave that propagates through the dielectric strip is leaked and radiated; and (c) a dielectric waveguide having a dielectric strip sandwiched between upper and lower parallel electrical conductors, wherein a vertically asymmetrical housing for leaking and radiating a high-frequency wave that propagates through the dielectric strip is provided on both sides or one side of the dielectric strip. Accordingly, the dielectric strip 3 is not provided with recessed portions unlike the conventional one, but is provided with only an asymmetrical housing. As a result, the manufacturing process becomes simple and the manufacturing cost can be reduced. Besides, since the dielectric strip is not provided with a plurality of recessed portions, unnecessary waves can be suppressed, so that frequency characteristic of input impedance can be improved and wider-bandwidth operation can be realized. Further, according to the preferred embodiments of the present invention, there is provided a leakage dielectric waveguide further comprising deflection means for deflecting the direction of radiation of a leaked and radiated high-frequency wave toward a predetermined direction, wherein the housing includes deflection means for deflecting the direction of radiation of a leaked and radiated high-frequency wave toward a predetermined direction or wherein the dielectric strip and the housing are so arranged that the leaked and radiated high-frequency wave is radiated toward a predetermined direction. With this arrangement, the radiated high-frequency wave can be deflected toward the same direction so as to be radiated with high radiation efficiency in a state of a substantially uniform electric field distribution and almost no residual power. Still further, according to the present preferred embodiment of present invention, there are provided plane antennas in which the above-mentioned leakage dielectric waveguide is combined with means for radiating a leaked and radiated high-frequency wave into free space. In this arrangement, a plane antenna which operates in wider bandwidth and with higher efficiency can be implemented, compared with the conventional plane antenna. The leakage dielectric waveguides and the plane antennas are described as ones for transmitting radio waves in the specification and the Claims attached to this specification, however, since the leakage dielectric waveguides and the plane antennas are reversible devices, they can be provided for receiving radio waves. That is, the leakage dielectric waveguides for receiving radio waves and the plane antenna for receiving radio waves are included in the scope of the Claims of the present application.

Claims: A leakage dielectric waveguide comprising: a housing made of plane-shaped parallel electrical conductors (1, 2) provided so as to be parallel to each other; a dielectric strip (3) for propagating a high-frequency wave between said parallel electrical conductors (1, 2), said dielectric strip (3) being provided within said housing; characterized in that said housing comprises an asymmetric portion (2s) formed in a direction perpendicular to the longitudinal direction of the dielectric strip (3) in a predetermined distance away from the dielectric strip (3) at which the strength of the electric field is relatively high, thereby leaking and radiating said high-frequency wave propagating through said dielectric strip. The leakage dielectric waveguide as claimed in Claim 1, wherein a step (2S) is formed in said housing. The leakage dielectric waveguide as claimed in Claim 1, wherein a further dielectric strip (6) is formed on said housing so as to be apart from said dielectric strip (3) and so that the longitudinal direction of said dielectric strip (3) is parallel to that of said further dielectric strip (6). The leakage dielectric waveguide as claimed in Claim 1, wherein a microstrip line is formed on said housing so as to be apart from said dielectric strip and so that the longitudinal direction of said dielectric strip is parallel to that of said microstrip line. The leakage dielectric waveguide as claimed in Claim 1, wherein a projecting electrical conductor is formed on said housing so as to vertically project into the inner part of said housing from the electrical conductor (2) on the surface of said dielectric strip (3). The leakage dielectric waveguide as claimed in Claim 1, wherein a dielectric slab is formed on said housing so as to be apart from said dielectric strip (3) and so that the longitudinal direction of said dielectric slab is perpendicular to that of said dielectric strip. The leakage dielectric waveguide as claimed in Claim 1, wherein a plurality of dielectric slabs are formed in parallel to each other at intervals of a propagation wavelenght of said high-frequency wave on one inner surface of said housing so as to be apart from said dielectric strip (3) and so that the longitudinal direction of said dielectric slabs is perpendicular to that of said dielectric strip (3). The leakage dielectric waveguide as claimed in Claim 1, wherein a plurality of first dielectric slabs are formed in parallel to each other at intervals of a propagation wavelenght of said high-frequency wave, on one inner surface of said housing so as to be apart from said dielectric strip (3) and so that the longitudinal direction of said first dielectric slabs is perpendicular to that of said dielectric strip, and wherein a plurality of second dielectric slabs are formed in parallel to each other at intervals of a propagation wavelength of said high-frequency wave and at half the position in the horizontal direction of said plurality of first dielectric slabs, on another inner surface of said housing so as to be apart from said dielectric strip (3) and so that the longitudinal direction of said second dielectric slabs is perpendicular to that of said delectric strip (3). The leakage dielectric waveguide as claimed in Claim 1, wherein said housing further comprises a side wall. The leakage dielectric waveguide as claimed in one of Claims 1 to 8, comprising: said dielectric strip (3) for propagating a high-frequency wave between said parallel electrical conductors (1, 2), said dielectric strip (3) being provided between said upper and lower parallel electrical conductors (1, 2): and said vertically asymmetrical housing for leaking and radiating said high-frequency wave propagating through said dielectric strip (3), said housing being provided on both sides or one side of said dielectric strip (3). The leakage dielectric waveguide as claimed in either one of Claims 1 to 10, further comprising deflection means for deflecting a direction of radiation of the leaked and radiated high-frequency wave toward a predetermined direction. The leakage dielectric waveguide as claimed in Claim 11, wherein said deflection means is a dielectric prism. The leakage dielectric waveguide as claimed in either one of Claims 1 to 10, wherein said housing includes deflection means for deflecting a direction of radiation of said leaked and radiated high-frequency wave toward a predetermined direction. The leakage dielectric waveguide as claimed in Claim 13, wherein said-deflection means is a dielectric prism. The leakage dielectric waveguid as claimed in either one of Claims 1 to 10, wherein said dielectric strip and said housing are arranged so that the leaked and radiated high-frequency wave is radiated toward a predetermined direction of radiation. A plane antenna comprising: at least one or a plurality of said leakage dielectric waveguides as claimed in either one of Claims 1 to 15, and means (10; 20) for radiating the leaked high-frequency wave into free space.

Inventors: ISHIKAWA YOUHEI, TANIZAKI TOHRU, YONEYAMA TSUKASA, ISHIKAWA, YOUHEI, TANIZAKI, TOHRU, YONEYAMA, TSUKASA, ISHIKAWA, YOUHEI, C/O MURATA MANUFACT. CO., LTD., TANIZAKI, TOHRU, C/O MURATA MANUFACT. CO., LTD.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1994
Main classification: H01Q21
IPC codes: H01Q13, H01P3, H01Q21